The present invention relates to a supporting apparatus for an objective lens used in an optical apparatus such as an optical scanner or the like or used in a data recording/reproducing apparatus which records/writes data with respect to an optical recording medium such as an optical disk drive, postscript type disk drive, phase change disk drive, CD-ROM, DVD, optical card, or the like, and also relates to a supporting apparatus for an optical element such as a galvano mirror or the like.
Conventionally, an optical element internally having a movable part or a movably supported optical element is used in various optical devices as described above. For example, in an optical element of an optical element such as a galvano mirror, an optical element such as an internal mirror or the like is supported to be rotatable and another optical element such as a objective lens which enables focus control is supported to be movable in a predetermined direction.
In many cases, a supporting apparatus based on a spring has been conventionally used as an apparatus for movably supporting an optical component or element of a small size. This type of supporting apparatus supports a movable part by a spring, and the movable part is supported to be rotated freely about a predetermined axis or moved freely in a predetermined direction by deformation of the spring. However, in this supporting apparatus based on a spring, when the movable part is rotated or moved, a restoring force is caused due to deformation of the spring, and therefore, there is a drawback that the movable part oscillates at a predetermined oscillation frequency so that resonance may occur when the movable part is driven.
To prevent this drawback, a damping mechanism is provided to apply a damping force to the oscillation of the movable portion. In a small size optical element or the like, a gel damping material is used as the damping mechanism. An example of the gel damping material is disclosed in Japanese Patent Application KOKAI Publication No. 6-314432.
FIGS. 20 to 21C show a basic structure of a damping mechanism using a conventional gel damping material as described above. Specifically, the reference 201 in the figures denotes a member in a fixed side, and a spring 202 made of a wire formed in U-shape is attached to an attachment portion 203 of the fixed side member 201. This spring 202 has a pair of leg portions 202a and 202b and a movable member (not shown) is supported at the top end portion of the leg portion 202a. For example, the movable member is supported to be rotatable or movable by twisting or bending the leg portion 202a to be deformed. The other leg portion 202b is not deformed.
Further, a gel damping material D is maintained between the leg portion 202a and the other leg portion 202b, for example. As the damping material D, for example, a thermosetting silicon gel material is used. To maintain the damping material D, a predetermined amount of silicon gel material in form of an unhardened liquid having fluidity is injected between the pair of leg portions 202a and 202b, and the lump of liquid D is maintained in a gap between the leg portions by the surface tension thereof. Further, thereafter, the entire part is heated by an oven or the like to harden the silicon gel material, forming the silicon gel material D in form of a gel.
Since the pair of leg portions 202a and 202b are embedded in the silicon gel material D in form of a gel, a damping force is generated due to viscosity of the silicon gel material D when one leg portion 202a and the other leg portion 202b are shifted relatively to each other by rotation or motion of the movable member.
Meanwhile, in case of maintaining a liquid silicon gel material D as described above between the leg portions, cohesion acts to minimize the free surface due to the surface tension in the liquid lump of the silicon gel material. Accordingly, in a direction perpendicular to the lengthwise directions of the leg portions 202a and 202b, the liquid lump of the silicon gel material is maintained to be stable in symmetrical positions and forms with respect to the center of the gap between the leg portions. However, in the lengthwise direction of the leg portions, the cross-sectional shapes of the leg portions and the distance therebetween are constant, and therefore, the area of the free surface is constant even if the liquid lump moves in the lengthwise direction. Accordingly, the unhardened silicon gel material injected into the gap can be maintained at an arbitrary position in the lengthwise direction so that the liquid lump unstably maintains its own position.
Therefore, in a conventional apparatus, the liquid lump of the silicon gel material D is positioned in the top end side of the other leg portion 202b as shown in FIG. 21A or in the center portion of the leg portion 202b as shown in FIG. 21B or shifted to the side of the fixed side member 201 as shown in FIG. 21C and maintained in the gap between the fixed side member 201 and the leg portions 202a and 202b. Accordingly, the position of the silicon gel material D in form of a gel formed by hardening such an unhardened silicon gel material is not constant. Therefore, variation of the damping characteristic appears in the supporting apparatus for the optical element or component, resulting in a drawback that the control accuracy is lowered. This drawback appears more notably as the size of the optical element or component becomes smaller and the accuracy thereof becomes higher.